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The influence of the sunspot cycle on phenomena at the bottom of the atmosphere
Planet. Space Sci. 1964, Vol. 12. pp. 327
to 331.
Perpamon Press Ltd. Printed in Northern Irdand
THE INFLUENCE OF THE SUNSPOT CYCLE ON PHENOMENA AT THE BOTTOM OF THE ATMOSPHERE C. W. ALLEN 1. INTRODUCTION
The Inter-Union Commission on Solar and Terrestrial Relationships has used the occasion of the URSI General Assembly in Tokyo, 1963, for some of its own scientific discussions. The first of these, on 4 September 1963, was devoted to the influences of the sunspot cycle on the lower atmosphere and is reported in this article. The discussion was prompted by the need for the Commission to keep abreast of what is perhaps the most longstanding and controversial of its topics. Since solar-weather-cycle problems have tended to bewilder scientists for over half a century no quick or clear conclusions could be expected. The literature on solar effects at the Earth’s surface is very extensive. Those meteorological and other factors that have been compared with sunspot changes are subject to large local fluctuations and consequently most comparisons covering a limited period of time give rise to apparent correlations. Without doubt many of the relations reported are of this character. Whether a particular result has any physical reality must be judged by the quality of the relation and whether it can pass any reasonable significance test. Until recently such tests have not been made and therefore rigorous analysts have been inclined to discard all early results as probably fortuitous. There can be no doubt that physically caused local variations can be large and that the vagaries of the weather do not of themselves demand any solar or cosmic origin. However there may be no need for each individual investigation to stand on its own significance test. It may contain valuable clues that can only be appreciated when many investigations are co-ordinated into a more widespread conclusion. The weakness of the subject at the present time is that there are no widespread conclusions that are generally accepted. Thus not only do individual investigations remain unto-ordinated but the investigators must face the possibility that their results will be considered fortuitous. To break through this impasse we need to establish a well proved solar cycle effect in either (a) some widespread meteorological data, or in (b) some surface atmosphere data for a restricted region. The first of these could be used for building together individual results, and the second would show beyond doubt that solar cycle influences are capable of penetrating or filtering through the upper atmosphere to produce detectable effects at the bottom. Our outlook on the whole subject becomes very dependent on whether we are able to regard either of these points as already proved. Without proof we are sceptical. With proof we can make progress. It is essential at this stage to watch for proof of high significance in any of the data studied. 2. METEOROLOGICAL
CORRELATIONS
The literature relating to solar effects on the weather has been reviewed from time to time in the Reports on Solar-Terrestrial Relations, notably by BrooksoA) and Bernard(j). These reviews are mainly assemblies of the many contributed results and they give an impression of the enormous amount of work that has been done in this field. The information set out in these reviews is in great need of further co-ordination and 327
328
C. W. ALLEN
synthesis. Fortunately in the Report of 1951(*)Brooks has made a serious attempt to decide what widespread conclusions could be accepted. The clearest results appear to be: (i) a negative correlation between tropical temperature and sunspots (ii) a positive correlation between pressure contrasts and sunspots (iii) a positive precipitation correlation where the pressure correlation is negative, and vice versa. If these results are found to be well supported in the data that has accumulated since Brooks’ article their validity would be virtually established. Many other data could then be reconsidered in relation to them. However it cannot be expected that any such widespread correlation could be of value for regional forecasting or day to day meteorological purposes. Studies based on restricted localities are perhaps more likely to give rise to strong correlations than studies of widespread areas. Without doubt the stimulus for many early analyses in this field has been the hope that in some special locality a meteorological factor would be found that was strongly influenced by the solar cycle. This would prove once and for all that solar activity could influence the lower atmosphere. The relation would provide a basis for local forecasting, and might allow the use of meteorological records for extending solar cycle data. Unfortunately there is no knowledge of any regional weather that is really dominated by the solar cycle. This situation is a matter of some importance because if good correlations cannot be found in any meteorological data it becomes very difficult to credit that such correlations can have penetrated into other ground level phenomena such as tree rings, lake levels, social phenomena etc.,whose interconnexion must be through theweather. Lesser correlations have no doubt been detected in many localities but most of these are still in need of statistical verification. 3. TREE RINGS AND THE SUNSPOT CYCLE
The following section of the report was prepared by D. K. Bailey after a visit to the Laboratory of Tree Ring Research of the University of Arizona, Tucson, from 5-8 December 1962. Exceptionally useful discussions were held with the Director, Dr. W. G. McGinnies, and with Dr. Harold C. Fritts, Dr. Bryant Bannister and Dr. C. W. Ferguson of the Laboratory staff. The time, indeed, appears ripe for a re-assessment of the solar effects problems, since much valuable work has been performed on collateral problems in the recent past and is continuing. It is now recognized that the principal pioneers in the field of dendrochronology, the late Dr. A. E. Douglass and the late Dr. Edmund Schulman, had at their disposal neither the modern statistical techniques required, nor the resources necessary in supporting areas of botany, ecology and climatology, to arrive at definitive conclusions as to the extent to which solar variation, as reflected for example by sunspot numbers, figures in the tree-ring patterns. It is now generally recognized that annual tree rings provide a record extending into the past of the collective effect of all the environmental factors which control the growth of a tree in a year. Available water and temperature are obviously important factors, but there are others. For example, there are cumulative factors which can carry over through two or more growing seasons. Thus the measured variability in ring width from year to year provides a measurement of the variability of the environmental factors as well as a record of accidental events which affect a tree. For example, trees in semi-arid regions such as the American southwest are sensitive to rainfall. If such trees grow on
INFLUENCE
OF SUNSPOT
CYCLE ON PHENOMENA
OF THE ATMOSPHERE
329
the sides of well-drained hills, ravines, or canyons, they may respond readily to immediate precipitation or run-off if the precipitation occurs at times when the temperatures are high enough to permit growth. On the other hand, a tree growing on low land or a valley bottom may subsist on underground water supplies whose short-term variability is inherently slight. In such cases “complacent” ring patterns are formed, i.e. patterns which show very little variability from year-to-year. Such trees may yield useful longterm information on such subjects as run-off, but do not respond sensitively, because of integration, to short-term variations in environment. It would appear that effects of solar variation, sometimes termed the solar cycle with a quasi-period of about 11 years, should not be sought in complacent trees. In the American southwest the Laboratory for Tree-Ring Research has established, through the careful selection and study of materials from archaeological sites, long chronologies which extend back to about 59 B.C. These are mainly based on Yellow Pine, Pinyon and Douglas Fir. In California the much more long-lived, but rather complacent, giant Sequoias have provided chronologies extending back to about 1200 B.C. More recently it has been discovered (by E. Schulman) that the Bristlecone Pine of the White Mountains of California can provide even longer chronologies, that are far from complacent. It is to be emphasized that different kinds of trees respond differently to a given environment, and much is being learned about these responses. Certainly much information concerning climatic variability is contained in the records provided by trees, in the form of annual rings, but the information is not easy to extract, and it is very important that statistical confidence be established and maintained at as high a level as possible during such information “salvaging” operations. Among all the unknown and varying environmental factors there is the known solar variation, back with high reliability to about 1830, with fair reliability to 1749, and crudely to about 1700. In studying the broad environmental aspects of tree rings it seems worthwhile to attempt to evaluate and remove from the data any effects which can be related directly to known solar variation. The problems of tree ring analysis have not thus far been approached from this viewpoint, and there are no satisfactory answers at present available. If satisfactory evidence can be found, through future analyses, a first objective as far as the IUCSTR is concerned would be to utilize the tree-ring material to establish the pattern of solar variation in the years before 1700, and as far backward as the available and useable tree-ring material permits. It had long been thought by Douglass that such information was extractable from tree-ring records. There is no more recent reason to suppose that it cannot. It does seem, however, that the task will not be simple. It is clear from this report that there is an enormous amount of long term meteorological information in the Laboratory of Tree Ring Research. This laboratory is itself fully committed with investigations on forest ecology and archaeological dating. Much information could be made available for solar studies if investigators could be found, and there is still promise of important and useful relations being uncovered. Quite apart from the sunspot cycle there is the possibility that variations of longer period could be detected. If this were so it is only the data covering thousands of years (such as tree rings) that could provide the necessary information and perhaps provide a link between recent meteorology and glaciation. The more recently studied Bristlecone Pines might be particularly useful from this point of view. It should be mentioned also that studies of varves in clays and polar ice cores present similar possibilities. The longer period solar cycles have recently been studied by Link@).
330
C. W. ALLEN
The opinion that a strong sunspot cycle effect is detectable in tree ring data can be traced to the A. E. Douglass researches”) and does not have recent backing. Douglass found some runs (in both recent and petrified samples) when an eleven year cycle appeared very clearly over a few cycles. To explain these runs we are faced with two unlikely alternatives, either (a) they are occasions when the solar cycle had a real and strong influence on tree rings, or (b) the cyclic effect is fortuitous in spite of being surprisingly regular and convincing. Any further investigation of the sunspot cycle in tree rings should look carefully into the circumstances of such occasions. The importance of maintaining the observational information for such researches was stressed by the Commission in the following recommendation : The Inter-Union Commission on Solar and Terrestrial Relationships seeks to encourage the harvesting of long series of terrestrial data concerning tree rings, varves in clays and polar ice cores with the view to detection and analysis of long term solar effects. 4. OTHER PHENOMENA POSSIBLY RELATED TO THE SOLAR CYCLE
In addition to the long term runs already mentioned there are many varied terrestrial phenomena in which the sunspot cycle appears to have been detected. These were not discussed in detail at the Commission Meeting but interest was expressed at the realistic nature of the correlations in certain cases. Reference was made to the levels of Lake Victoria studied by Brooks(*). The lake level variations, like those of tree rings, must be caused by variations in meteorological factors and any correlation with the solar cycle should show at least as well in the meteorological as any other data. However no meteorological data show the cycle effects as strongly as some of the secondary measurements such as lake levels. Reference was also made to two sets of observations that are apparently related to chemical activity, (a) the chemical tests by Piccardi@), and the storage battery factors by Barbero”). To suggest any specific feature of the solar cycle that could affect the relevant chemical reactions appears quite fanciful, but the relation of the results to the sunspot cycle do not at the present time look fortuitous. In the case of the chemical tests the observations of the coming sunspot minimum will probably clarify the situation. Experiments are being carried out by Dr. Lodge at the National Centre for Atmospheric Research to obtain a clearer understanding of the physico-chemical process in Piccardi’s observations. 5. RECENT RESULTS, DEVELOPMENTS
AND CONSIDERATIONS
For recent developments this report is largely dependent on notes submitted by Roberts and reference to his recent review’ll). The greatest promise of relating the lower atmosphere to solar activity is through the intermediary of the upper atmosphere. Studies of circulation at the 500 mb and 300 mb pressure levels show fairly clear relations with geomagnetic storms and therefore secondarily with the sunspot cycle (13p13).Of particular interest is the relation between trough development in the Gulf of Alaska and aurorae. Since the Gulf of Alaska is a breeding ground for troughs which later move eastward a connexion with widespread meteorology is possible. Neyo4) has suggested that changes in ionization produced by cosmic radiation could have considerable effects in the stratosphere and may influence the troposphere. This raises the question of whether there is any possibility of detecting, (a) any unusual isotope distribution in otherwise dateable organic material which could indicate very large specific cosmic ray events, and (b) the sunspot cycle influenced galactic cosmic ray variations in growing organic material.
INFLUENCE
OF SUNSPOT CYCLE ON PHENOMENA OF THE ATMOSPHERE
331
The facilities for numerical analysis of correlations have greatly improved in recent years but the forms of analysis still need consideration. It was emphasized that it isnecessary to allow for the variation of period in solar data which means that formal harmonic analysis is not directly applicable. It should also be remembered that local variations are not necessarily random and that any significance test that assumes randomness may give a faulty result. In particular a slow secular change in two simultaneous variables leads to an apparent correlation which may not be physically real. 6. CONCLUSION
The general conclusion of the discussion was that the possibilities of detecting solar terrestrial relations and using surface data for solar studies has not yet been thoroughly explored. Information is being assembled rapidly and there are vastly improved means for dealing with it. There are still bathing misunderstandings to be clarified and there is still a reasonable expectation that useful and illuminating relations are to be uncovered. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
C. E. P. BROOKS, 1st Report on Solar Terrestrial Relations, p. 66 (1926). C. E. P. BROOKS,4th Report on Solar Terrestrial Relations, p. 147 (1936). C. E. P. BROOKS,5th Report on Solar Terrestrial Relations, p. 196 (1939). C. E. P. BROOKS,7th Report on Solar Terrestrial Relations, p. 183 (1951). P. BERNARD,9th Report on Solar Terrestrial Relations, p. 111 (1957). F. LINK, 10th Report on Solar Terrestrial Relations, Planet. Space Sci. 12, 333 (1964). A. E. DOUOLASS,Climatic Cycles and Tree Growth, Pub. No. 289. Carnegie Inst. 1 (1919); 2 (1928); 3, (1936). Especially 1. p. 74, Plate 8. C. E. P. BROOKS,Met. Ofice Geophys. Mem. No. 20 (1923). Later data in F. DIXIW, Proc. Inst. Civ. Erg. 10,214(1958). G. PICCARDI, Pub. d’fnst. Nar. Ottica ZV, No. 344, Arcetri-Firenze (1961). D. R. BARBER,Nature, Land. 195,684 (1962). W. 0. ROBERTS,Proceedings of the 1962 Berlin Symposium on Stratospheric Circulation. N. J. MACDONALD and W. 0. ROBERTS,J. Geophys. Res. 65,529 (1960). TWITCHELL,Bull. Geophys., Montreal No. 13,69 (1963). E. P. NEY, Nature, Land. 183,451 (1959).
to 331.
Perpamon Press Ltd. Printed in Northern Irdand
THE INFLUENCE OF THE SUNSPOT CYCLE ON PHENOMENA AT THE BOTTOM OF THE ATMOSPHERE C. W. ALLEN 1. INTRODUCTION
The Inter-Union Commission on Solar and Terrestrial Relationships has used the occasion of the URSI General Assembly in Tokyo, 1963, for some of its own scientific discussions. The first of these, on 4 September 1963, was devoted to the influences of the sunspot cycle on the lower atmosphere and is reported in this article. The discussion was prompted by the need for the Commission to keep abreast of what is perhaps the most longstanding and controversial of its topics. Since solar-weather-cycle problems have tended to bewilder scientists for over half a century no quick or clear conclusions could be expected. The literature on solar effects at the Earth’s surface is very extensive. Those meteorological and other factors that have been compared with sunspot changes are subject to large local fluctuations and consequently most comparisons covering a limited period of time give rise to apparent correlations. Without doubt many of the relations reported are of this character. Whether a particular result has any physical reality must be judged by the quality of the relation and whether it can pass any reasonable significance test. Until recently such tests have not been made and therefore rigorous analysts have been inclined to discard all early results as probably fortuitous. There can be no doubt that physically caused local variations can be large and that the vagaries of the weather do not of themselves demand any solar or cosmic origin. However there may be no need for each individual investigation to stand on its own significance test. It may contain valuable clues that can only be appreciated when many investigations are co-ordinated into a more widespread conclusion. The weakness of the subject at the present time is that there are no widespread conclusions that are generally accepted. Thus not only do individual investigations remain unto-ordinated but the investigators must face the possibility that their results will be considered fortuitous. To break through this impasse we need to establish a well proved solar cycle effect in either (a) some widespread meteorological data, or in (b) some surface atmosphere data for a restricted region. The first of these could be used for building together individual results, and the second would show beyond doubt that solar cycle influences are capable of penetrating or filtering through the upper atmosphere to produce detectable effects at the bottom. Our outlook on the whole subject becomes very dependent on whether we are able to regard either of these points as already proved. Without proof we are sceptical. With proof we can make progress. It is essential at this stage to watch for proof of high significance in any of the data studied. 2. METEOROLOGICAL
CORRELATIONS
The literature relating to solar effects on the weather has been reviewed from time to time in the Reports on Solar-Terrestrial Relations, notably by BrooksoA) and Bernard(j). These reviews are mainly assemblies of the many contributed results and they give an impression of the enormous amount of work that has been done in this field. The information set out in these reviews is in great need of further co-ordination and 327
328
C. W. ALLEN
synthesis. Fortunately in the Report of 1951(*)Brooks has made a serious attempt to decide what widespread conclusions could be accepted. The clearest results appear to be: (i) a negative correlation between tropical temperature and sunspots (ii) a positive correlation between pressure contrasts and sunspots (iii) a positive precipitation correlation where the pressure correlation is negative, and vice versa. If these results are found to be well supported in the data that has accumulated since Brooks’ article their validity would be virtually established. Many other data could then be reconsidered in relation to them. However it cannot be expected that any such widespread correlation could be of value for regional forecasting or day to day meteorological purposes. Studies based on restricted localities are perhaps more likely to give rise to strong correlations than studies of widespread areas. Without doubt the stimulus for many early analyses in this field has been the hope that in some special locality a meteorological factor would be found that was strongly influenced by the solar cycle. This would prove once and for all that solar activity could influence the lower atmosphere. The relation would provide a basis for local forecasting, and might allow the use of meteorological records for extending solar cycle data. Unfortunately there is no knowledge of any regional weather that is really dominated by the solar cycle. This situation is a matter of some importance because if good correlations cannot be found in any meteorological data it becomes very difficult to credit that such correlations can have penetrated into other ground level phenomena such as tree rings, lake levels, social phenomena etc.,whose interconnexion must be through theweather. Lesser correlations have no doubt been detected in many localities but most of these are still in need of statistical verification. 3. TREE RINGS AND THE SUNSPOT CYCLE
The following section of the report was prepared by D. K. Bailey after a visit to the Laboratory of Tree Ring Research of the University of Arizona, Tucson, from 5-8 December 1962. Exceptionally useful discussions were held with the Director, Dr. W. G. McGinnies, and with Dr. Harold C. Fritts, Dr. Bryant Bannister and Dr. C. W. Ferguson of the Laboratory staff. The time, indeed, appears ripe for a re-assessment of the solar effects problems, since much valuable work has been performed on collateral problems in the recent past and is continuing. It is now recognized that the principal pioneers in the field of dendrochronology, the late Dr. A. E. Douglass and the late Dr. Edmund Schulman, had at their disposal neither the modern statistical techniques required, nor the resources necessary in supporting areas of botany, ecology and climatology, to arrive at definitive conclusions as to the extent to which solar variation, as reflected for example by sunspot numbers, figures in the tree-ring patterns. It is now generally recognized that annual tree rings provide a record extending into the past of the collective effect of all the environmental factors which control the growth of a tree in a year. Available water and temperature are obviously important factors, but there are others. For example, there are cumulative factors which can carry over through two or more growing seasons. Thus the measured variability in ring width from year to year provides a measurement of the variability of the environmental factors as well as a record of accidental events which affect a tree. For example, trees in semi-arid regions such as the American southwest are sensitive to rainfall. If such trees grow on
INFLUENCE
OF SUNSPOT
CYCLE ON PHENOMENA
OF THE ATMOSPHERE
329
the sides of well-drained hills, ravines, or canyons, they may respond readily to immediate precipitation or run-off if the precipitation occurs at times when the temperatures are high enough to permit growth. On the other hand, a tree growing on low land or a valley bottom may subsist on underground water supplies whose short-term variability is inherently slight. In such cases “complacent” ring patterns are formed, i.e. patterns which show very little variability from year-to-year. Such trees may yield useful longterm information on such subjects as run-off, but do not respond sensitively, because of integration, to short-term variations in environment. It would appear that effects of solar variation, sometimes termed the solar cycle with a quasi-period of about 11 years, should not be sought in complacent trees. In the American southwest the Laboratory for Tree-Ring Research has established, through the careful selection and study of materials from archaeological sites, long chronologies which extend back to about 59 B.C. These are mainly based on Yellow Pine, Pinyon and Douglas Fir. In California the much more long-lived, but rather complacent, giant Sequoias have provided chronologies extending back to about 1200 B.C. More recently it has been discovered (by E. Schulman) that the Bristlecone Pine of the White Mountains of California can provide even longer chronologies, that are far from complacent. It is to be emphasized that different kinds of trees respond differently to a given environment, and much is being learned about these responses. Certainly much information concerning climatic variability is contained in the records provided by trees, in the form of annual rings, but the information is not easy to extract, and it is very important that statistical confidence be established and maintained at as high a level as possible during such information “salvaging” operations. Among all the unknown and varying environmental factors there is the known solar variation, back with high reliability to about 1830, with fair reliability to 1749, and crudely to about 1700. In studying the broad environmental aspects of tree rings it seems worthwhile to attempt to evaluate and remove from the data any effects which can be related directly to known solar variation. The problems of tree ring analysis have not thus far been approached from this viewpoint, and there are no satisfactory answers at present available. If satisfactory evidence can be found, through future analyses, a first objective as far as the IUCSTR is concerned would be to utilize the tree-ring material to establish the pattern of solar variation in the years before 1700, and as far backward as the available and useable tree-ring material permits. It had long been thought by Douglass that such information was extractable from tree-ring records. There is no more recent reason to suppose that it cannot. It does seem, however, that the task will not be simple. It is clear from this report that there is an enormous amount of long term meteorological information in the Laboratory of Tree Ring Research. This laboratory is itself fully committed with investigations on forest ecology and archaeological dating. Much information could be made available for solar studies if investigators could be found, and there is still promise of important and useful relations being uncovered. Quite apart from the sunspot cycle there is the possibility that variations of longer period could be detected. If this were so it is only the data covering thousands of years (such as tree rings) that could provide the necessary information and perhaps provide a link between recent meteorology and glaciation. The more recently studied Bristlecone Pines might be particularly useful from this point of view. It should be mentioned also that studies of varves in clays and polar ice cores present similar possibilities. The longer period solar cycles have recently been studied by Link@).
330
C. W. ALLEN
The opinion that a strong sunspot cycle effect is detectable in tree ring data can be traced to the A. E. Douglass researches”) and does not have recent backing. Douglass found some runs (in both recent and petrified samples) when an eleven year cycle appeared very clearly over a few cycles. To explain these runs we are faced with two unlikely alternatives, either (a) they are occasions when the solar cycle had a real and strong influence on tree rings, or (b) the cyclic effect is fortuitous in spite of being surprisingly regular and convincing. Any further investigation of the sunspot cycle in tree rings should look carefully into the circumstances of such occasions. The importance of maintaining the observational information for such researches was stressed by the Commission in the following recommendation : The Inter-Union Commission on Solar and Terrestrial Relationships seeks to encourage the harvesting of long series of terrestrial data concerning tree rings, varves in clays and polar ice cores with the view to detection and analysis of long term solar effects. 4. OTHER PHENOMENA POSSIBLY RELATED TO THE SOLAR CYCLE
In addition to the long term runs already mentioned there are many varied terrestrial phenomena in which the sunspot cycle appears to have been detected. These were not discussed in detail at the Commission Meeting but interest was expressed at the realistic nature of the correlations in certain cases. Reference was made to the levels of Lake Victoria studied by Brooks(*). The lake level variations, like those of tree rings, must be caused by variations in meteorological factors and any correlation with the solar cycle should show at least as well in the meteorological as any other data. However no meteorological data show the cycle effects as strongly as some of the secondary measurements such as lake levels. Reference was also made to two sets of observations that are apparently related to chemical activity, (a) the chemical tests by Piccardi@), and the storage battery factors by Barbero”). To suggest any specific feature of the solar cycle that could affect the relevant chemical reactions appears quite fanciful, but the relation of the results to the sunspot cycle do not at the present time look fortuitous. In the case of the chemical tests the observations of the coming sunspot minimum will probably clarify the situation. Experiments are being carried out by Dr. Lodge at the National Centre for Atmospheric Research to obtain a clearer understanding of the physico-chemical process in Piccardi’s observations. 5. RECENT RESULTS, DEVELOPMENTS
AND CONSIDERATIONS
For recent developments this report is largely dependent on notes submitted by Roberts and reference to his recent review’ll). The greatest promise of relating the lower atmosphere to solar activity is through the intermediary of the upper atmosphere. Studies of circulation at the 500 mb and 300 mb pressure levels show fairly clear relations with geomagnetic storms and therefore secondarily with the sunspot cycle (13p13).Of particular interest is the relation between trough development in the Gulf of Alaska and aurorae. Since the Gulf of Alaska is a breeding ground for troughs which later move eastward a connexion with widespread meteorology is possible. Neyo4) has suggested that changes in ionization produced by cosmic radiation could have considerable effects in the stratosphere and may influence the troposphere. This raises the question of whether there is any possibility of detecting, (a) any unusual isotope distribution in otherwise dateable organic material which could indicate very large specific cosmic ray events, and (b) the sunspot cycle influenced galactic cosmic ray variations in growing organic material.
INFLUENCE
OF SUNSPOT CYCLE ON PHENOMENA OF THE ATMOSPHERE
331
The facilities for numerical analysis of correlations have greatly improved in recent years but the forms of analysis still need consideration. It was emphasized that it isnecessary to allow for the variation of period in solar data which means that formal harmonic analysis is not directly applicable. It should also be remembered that local variations are not necessarily random and that any significance test that assumes randomness may give a faulty result. In particular a slow secular change in two simultaneous variables leads to an apparent correlation which may not be physically real. 6. CONCLUSION
The general conclusion of the discussion was that the possibilities of detecting solar terrestrial relations and using surface data for solar studies has not yet been thoroughly explored. Information is being assembled rapidly and there are vastly improved means for dealing with it. There are still bathing misunderstandings to be clarified and there is still a reasonable expectation that useful and illuminating relations are to be uncovered. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
C. E. P. BROOKS, 1st Report on Solar Terrestrial Relations, p. 66 (1926). C. E. P. BROOKS,4th Report on Solar Terrestrial Relations, p. 147 (1936). C. E. P. BROOKS,5th Report on Solar Terrestrial Relations, p. 196 (1939). C. E. P. BROOKS,7th Report on Solar Terrestrial Relations, p. 183 (1951). P. BERNARD,9th Report on Solar Terrestrial Relations, p. 111 (1957). F. LINK, 10th Report on Solar Terrestrial Relations, Planet. Space Sci. 12, 333 (1964). A. E. DOUOLASS,Climatic Cycles and Tree Growth, Pub. No. 289. Carnegie Inst. 1 (1919); 2 (1928); 3, (1936). Especially 1. p. 74, Plate 8. C. E. P. BROOKS,Met. Ofice Geophys. Mem. No. 20 (1923). Later data in F. DIXIW, Proc. Inst. Civ. Erg. 10,214(1958). G. PICCARDI, Pub. d’fnst. Nar. Ottica ZV, No. 344, Arcetri-Firenze (1961). D. R. BARBER,Nature, Land. 195,684 (1962). W. 0. ROBERTS,Proceedings of the 1962 Berlin Symposium on Stratospheric Circulation. N. J. MACDONALD and W. 0. ROBERTS,J. Geophys. Res. 65,529 (1960). TWITCHELL,Bull. Geophys., Montreal No. 13,69 (1963). E. P. NEY, Nature, Land. 183,451 (1959).